The techniques of packing a load by wrapping have as their principal function to endow the load formed as a pile with the necessary cohesion so as to preserve the stability of the pile at the time of its handling.
The method used to ensure this cohesion is a drawable film which is wound in the drawn state around the pile under a predetermined amount of low tension, the film having a tendency to retract slightly and to lie flat on the load. In general, at least two layers of winding are effected.
Among the machines used for the implementation of this packing technique, there are those in which the load revolves in relation to a fixed source of supply of pre-drawn film, and those in which the load is fixed, with the film-supply source revolving around such load. In these two categories, the film supply source comprises a spool of film combined with a pre-drawing device and is vertically mobile along its support (if the axis of the load is vertical) so as to be able to sweep the entire height of the load with a helicoidal winding.
The main problems still to be resolved for this type of machine relate to the beginning and end of a wrapping cycle. Indeed, at the beginning of each cycle, it is necessary to make the end of the film integral with the load so that the unwinding of this film results from the relative revolution of the load and the film-supply source. It is necessary, at the end of the cycle, to cut the film by "attaching" one of the ends to the load while the other end is preserved so as to then be applied to a subsequent load.